Using tabular AgX emulsion grains in a photographic material gives improved color sensitivity, sharpness, light scattering, covering power, development progression, graininess, etc., compared with using non-tabular AgX grains. Therefore, tabular grains having twin planes parallel to each other and having {100} faces as major faces mainly have been used.
However, when a large amount of sensitizing dye is adsorbed onto AgX grains, grains having {100} faces normally show better color sensitizing properties. Accordingly, the development of the tabular grains having {100} faces as major faces has been desired. Tabular grains having {100} faces wherein the shapes of the major faces are right angled parallelograms are disclosed in JP-A-51-88017 (the term "JP-A" as used herein means a "published, unexamined Japanese patent application"), JP-B-64-8323 (the term "JP-B" as used herein means an "examined Japanese patent publication") , EP 0534395A1, U.S. Pat. No. 5,292,632, U.S. Pat. No. 5,264,337, U.S. Pat. No. 5,320,938 and JP-A-6-59360. However, all of these grains have nuclei during nucleus formation (hereinafter referred to as "nucleus" (or "nuclei")) at the center of the grains or the positions of the nuclei are not defined clearly. When the nuclei are at the center of the grains, the grains are inferior in anisotropic growth and difficult to grow in terms of keeping thickness small. Such grains also have the drawback of grain formation of even thickness being difficult. The description that grains grow by dislocation is disclosed in Journal of Crystal Growth, 23 (1974), pages 207 to 213, but the direction of the dislocation line in that article is in the {100} direction parallel to the side face of the grain and differs from the direction of the dislocation line of the grain of the present invention. When the anisotropic growth of the grain begins at the dislocation line extending to the {100} direction, the grain has, in general, a sectorial shape with one corner of the main plane being rounded in shape, therefore, inferior in anisotropic growth.
In the medical field in recent years, the replenishment rate of replenishers has been reduced in view of environmental protection and space-saving. However, the reduced replenishment rate increases the accumulated amount of substances dissolved from photographic materials, leading to deteriorated photographic performance. In particular, surfactants are used in a large amount as an electrostatic characteristic improving agent, and dissolved-out substances accumulate in processing solutions and cause foaming, leading to development unevenness.
Forming images using tabular grains having {100} faces as major faces by UV light exposure gives insufficient sharpness.
The present inventors have found as a result of extensive studies that it is effective to use high silver chloride content tabular grains having less light scattering even in a UV light exposure range and having higher light transmitting property compared to silver bromide in order to increase image sharpness. However, images are blurred and sharpness decreases by these methods alone due to halation and crossover light when the photographic material to be used has light-sensitive layers on both sides of the support. With respect to the halation and crossover light effects, tabular grains having higher silver chloride contents are affected rather largely because of their smaller light absorption coefficient and larger light transmitting property. The present inventors have found that by using a UV absorbing agent this problem could be solved and excellent sharpness could be obtained.
In addition, it also has been found that because such a constitution has no use for spectral sensitizing dyes and crossover cut dyes in the visible region, problems such as the contamination of processing solutions with colors, dyes and decomposed products thereof by rapid processing and reduced replenisher processing or coloring of photographic materials by their remaining in photographic materials do not arise. Therefore, an ideal system is feasible.
Further, although silver chloride tabular grains are excellent for rapid processing and in fixing properties and the like as described in the prior art, at the same time, the light absorption coefficient increases by UV light exposure. As a result, light absorption by the grains in the upper layer increases and the quantity of light to be absorbed by the grains in the lower layer decreases. As a result, photographic materials become relatively low contrast. When photographic materials are low contrast, the contrast of images formed lowers and visual sharpness reduces. This problem is more conspicuous in the silver bromide system in which light absorption reaches long wave. To cope with this problem regarding UV light, methods of increasing light transmitting property by using tabular silver bromide grains or using silver chloride are disclosed, for example, in WO 93/01521. However, sufficiently high gradation cannot be obtained by these methods.
Accordingly, a photographic material having a curve of high visual sharpness and high gradation in combination with a fluorescent intensifying screen emitted by UV light exposure had not been realized. As a result of extensive studies in these circumstances, the present inventors have found that a photographic material having higher contrast can be constituted not only by increasing the transmittance of silver halide grains by raising the silver chloride content and making grains tabular so that UV light can sufficiently reach the lower layer, but also adopting a multilayer structure with the emulsion layer of the highest sensitivity being disposed as the lower layer. Moreover, in super rapid processing of the total processing time of dry to dry of less than 60 seconds, when the high sensitivity emulsion layer is disposed as a lower layer, in general, diffusion of the developing solution is slow and the intrinsic performance of the high sensitivity emulsion cannot be developed and the sensitivity is reduced. Therefore, sufficiently high contrast images cannot be formed. However, it has been found, beyond our expectation, that by using tabular grains having a high silver chloride content as in the present invention, the high sensitivity emulsion in the lower layer exhibits intrinsic photographic performance and high contrast images can be formed. Further, it has been found that such a phenomenon is particularly effective in X-ray image formation using a fluorescent intensifying screen emitted by UV light exposure.